1. Field of the Invention
This invention relates to an improved sedimentation procedure and more particularly to a method for the rapid settling of fine mineral particles from aqueous suspensions.
2. Description of the Prior Art
The prior art is well aware of the so-called wet process phosphoric acid systems in which phosphate ores such as phosphate rock and similar minerals are treated with a strong mineral acid such as sulfuric acid to effect acidulation of the rock and result in the production of phosphoric acid and a calcium sulfate precipitate usually called gypsum. U.S. Pat. Nos. 3,699,212 and 3,859,423 exemplify processes of this type. The basic mineral phosphate rock used in this process contains a substantial amount of silica materials in various forms and during the reaction, a substantial amount of materials, generally referred to as a phosphate slime slurry, is formed as a by-product, which by-product generally comprises a non-settling fine particle suspension containing various siliceous materials which are a combination of silicate minerals, for example attapulgite, montmorillonite and kaolinite clays. Because of the intricate network of the various clay materials within the slime system, the system is highly resistant to settling and therefore has usually been transferred to a settling pond where it may be permitted to stand for long periods of time in the hope that eventual settling will occur. However, because of recent thrusts in the areas of ecology, the leaching of the slimes by rain water and other nature systems has caused science to look for ways in which more rapid settling of the slime mixtures may be effected. The present invention provides a means by which the slime systems can be settled rapidly to result in fine particles of the minerals contained therein.
U.S. Pat. No. 3,493,340 to Bosen et al relates to the treatment of phosphate ore generally in the manner described and specifically teaches that the phosphate rock which is reacted with sulfuric acid contains fluoride, magnesium, silica and the like, and that various complexes of such solutions remain in the mixture and are difficult to remove. This patent is particularly concerned with magnesium impurities and does not suggest procedures for treating the resulting slime systems.
A more pertinent patent to the subject matter of the present invention is U.S. Pat. No. 3,061,541 to Henry which relates to the treatment of potable waters to separate suspended solids from the water. According to this patent an activated silica sol containing fluoride ions is produced by contacting a solution of sodium silicofluoride with sodium silicate, and then introducing the resulting reaction mixture into raw water to produce floc formation, clarification and fluoridation of the water. This patent however does not disclose the treatment of suspensions of the type described herein.